Buggy code:
public boolean hashTableHasValue ( int table , int value ) { } public int hashTableIndex ( int table , CharSequence key ) { } public int hashCode ( CharSequence value ) { } public int hashTableIndex ( int table , int key ) { } public boolean hashTableIsEmpty ( int table ) { } public int hashTableKeys ( int table ) { } public void hashTablePut ( int table , int key , int value ) { } public int hashTableRemove ( int table , int key ) { } public String hashTableToString ( int table ) { } public static final int threadId ( int thread ) { } public static final String threadToString ( int word ) { } public int copy ( int value ) { } public int copyArray ( int array ) { } public int copyAttribute ( int att ) { } public int copyBucket ( int bucket ) { } public int copyBuffer ( int buffer ) { } public int copyBufferStorage ( int arrays ) { } public int copyCodeBox ( int codeBox ) { } public void copyContStack ( int cont ) { } public int copyFun ( int fun ) { } public int copyHashTable ( int table ) { } public int copyHashTableBucket ( int bucket ) { } public int copyObj ( int obj ) { } public int copyString ( int s ) { } public boolean equalFloats ( int f1 , int f2 ) { } public boolean equalNumbers ( int n1 , int n2 ) { } public boolean equalRefPaths ( int p1 , int p2 ) { } public boolean equalSets ( int set1 , int set2 ) { } public boolean subSet ( int set1 , int set2 ) { } public boolean equalStrings ( int s1 , int s2 ) { } public boolean equalValues ( int v1 , int v2 ) { } public synchronized void perform ( ) { } public void handleArrayException ( ) { } public void handleThrow ( Throwable throwable ) { } public void performInstrs ( ) { } public void hasSlot ( ) { } public void objHasSlot ( int obj , int slot ) { } public void line ( int line ) { } public void cons ( ) { } public void mkSeqFrom ( int length ) { } public void mkSetFrom ( int length ) { } public void add ( ) { } public int addInts ( int i , int j ) { } public void overloadedBinOp ( int v1 , int v2 , String op ) { } public int consAppend ( int l1 , int l2 ) { } private int addArrays ( int v1 , int v2 ) { } public void sub ( ) { } public void mul ( ) { int v1 = valueStack . elements [ ( -- ( valueStack . index ) ) ] ; int v2 = valueStack . elements [ ( -- ( valueStack . index ) ) ] ; boolean v1IsInt = ( v1 > > 24 ) == ( INT ) ; boolean v1IsNegInt = ( v1 > > 24 ) == ( NEGINT ) ; boolean v2IsInt = ( v2 > > 24 ) == ( INT ) ; boolean v2IsNegInt = ( v2 > > 24 ) == ( NEGINT ) ; if ( ( v1IsInt || v1IsNegInt ) && ( v2IsInt || v2IsNegInt ) ) <START_BUG> valueStack . push ( mulInts ( ( v1IsNegInt || v2IsNegInt ) , Machine . value ( v1 ) , Machine . value ( v2 ) ) ) ; <END_BUG> else if ( ( Machine . isFloat ( v1 ) ) && ( Machine . isFloat ( v2 ) ) ) valueStack . push ( floatMul ( v2 , v1 ) ) ; else if ( ( Machine . isBigInt ( v1 ) ) && ( Machine . isBigInt ( v2 ) ) ) valueStack . push ( asBigInt ( asBigInteger ( v1 ) . multiply ( asBigInteger ( v2 ) ) ) ) ; else if ( ( Machine . isBigInt ( v1 ) ) && ( v2IsInt || v2IsNegInt ) ) valueStack . push ( asBigInt ( asBigInteger ( v1 ) . multiply ( asBigInteger ( mkBigInt ( Machine . intValue ( v2 ) ) ) ) ) ) ; else if ( ( v1IsInt || v1IsNegInt ) && ( Machine . isBigInt ( v2 ) ) ) valueStack . push ( asBigInt ( asBigInteger ( mkBigInt ( Machine . intValue ( v1 ) ) ) . multiply ( asBigInteger ( v2 ) ) ) ) ; else overloadedBinOp ( v2 , v1 , "mul" ) ; } public int mulInts ( boolean isNegative , int i , int j ) { } public void div ( ) { } public int intSlash ( int i1 , int i2 ) { } public int bigIntDiv ( int v1 , int v2 ) { } public void gre ( ) { } public void less ( ) { } public void eql ( ) { } public void and ( ) { } public void implies ( ) { } public int implies ( int v1 , int v2 ) { } public void or ( ) { } public void not ( ) { } public void dot ( int name ) { } public void dot ( int name , int obj ) { } public void dotCollection ( int name , int collection ) { } public void dotDaemon ( int name , int daemon ) { } public void dotForeignFun ( int name , int fun ) { } public void dotForeignObj ( int name , int obj ) { } public void dotFun ( int name , int fun ) { } public void dotObj ( int name , int obj ) { }

Fix:
valueStack . push ( mulInts ( ( v1IsNegInt ^ v2IsNegInt ) , Machine . value ( v1 ) , Machine . value ( v2 ) ) ) ;